The invention relates to a tool gripper to remove and position a tool from or in a work spindle or a tool magazine.
In program-controlled milling and drilling machines and in machining centers as well, different tool changing systems are used to take-off the individual tools from the respective work spindle and to deposit them in a tool magazine positioned at a predetermined distance and vice versa. An important component of the various tool changing systems are the tool grippers, which have to provide for a safe hold of the possibly heavy tools when they are pulled off the spindle, when various transport movements are carried out, and also when the spindle is put in the predetermined position in the tool magazine. Therefore, known grippers regularly have motor-driven driving means for the opening and closing movements of the tong-like gripper arms which normally hold the arms at a bracing position which is sufficiently widely opened and, when the positioning on the tool has been carried out, provide a sufficiently powerful closing movement. A disadvantage of these operating devices which are mostly hydraulic cylinders is their complex structure and their susceptibility to trouble after prolonged use which could lead to an unintentional opening of the gripper arms during a transport movement under certain circumstances. Such a malfunction regularly results in switching-off the machine which involves the further danger that the expensive tools or the clamped work pieces, respectively, are damaged.